Description

A very reproducible bug where the body of a HTTPS POST request is never forwarded to the origin server.

Client submits a HTTPS POST request to TS, which is supposed to forward to the backend/origin server via HTTP. TS process the HTTP headers and establishes connection to the origin server, but the body of the HTTPS POST is never read. This hangs until the client times out and shuts down the connection.

To reproduce:

Client connects to TS using HTTPS (works OK if it is just HTTP).

It must be a POST request.

TS must use at least 2 worker threads.

Easier to reproduce when the connections to the origin server is HTTP (not HTTPS).

POST body must be large enough so that the HTTP request headers and POST body do NOT fit within the same TCP packet. (2000 bytes is a good size)

I can consistently reproduce this problem using 2 separate clients each simultaneously submitting 2 requests back to back (i.e., 2 requests from each client, a total of 4 requests). This gives you a high probability that at least one of the requests would hang.

Observation:

Thread A accepted and processed the HTTP headers, and called "UnixNetProcessor::connect_re" to prepare a new connection to the origin server.

Thread A must not have read the body of the POST. Otherwise, it works fine.

Thread B was assigned the task to handle the origin server connection. If the same thread A was picked, then everything works fine.

Apparently, one of the first things that thread B does is to acquire the mutex for reading from the client. (Why does it do that??)

While thread B was holding the mutex, thread A proceeded in "SSLNetVConnection::net_read_io", tried and failed to acquire the mutex. Thread A typically re-tried calling "SSLNetVConnection::net_read_io" soon, but gave up after the second failure. But if thread B released the mutex soon enough, that thread A could proceed happily and everything works.

From this point, the body of the POST is never read from the client, and there is nothing to be proxy'd to the origin server, and both the consumer and producer tasks are never scheduled to run again – or until the client times out. I tried setting the client-side time out to as long as 3-5 minutes and TS really does not recover by itself until the client closed the connection.

This is the first time I uses this bug system. Please let me know how I could produce the configuration files and trace logs, etc. Thanks!

Interesting.Did you try turning off sharing origin connections (or setting it to "2", which creates a connection pool per thread)? Not saying that's a "fix", but curious to hear if it helps (and if it does, it's a viable work around).

Leif Hedstrom
added a comment - 07/Jan/12 05:02 Interesting.Did you try turning off sharing origin connections (or setting it to "2", which creates a connection pool per thread)? Not saying that's a "fix", but curious to hear if it helps (and if it does, it's a viable work around).
I'll also look at your suggested patch, and see if it makes sense
Thanks!
– leif